Bio-recycling of metals: Recycling of technical products using biological applications

The increasing demand of different essential metals as a consequence of the development of new technologies, especially in the so called “low carbon technologies” require the development of innovative technologies that enable an economic and environmentally friendly metal recovery from primary and secondary resources. There is serious concern that the demand of some critical elements might exceed the present supply within a few years, thus necessitating the development of novel strategies and technologies to meet the requirements of industry and society. Besides an improvement of exploitation and processing of ores, the more urgent issue of recycling of strategic metals has to be enforced. However, current recycling rates are very low due to the increasing complexity of products and the low content of certain critical elements, thus hindering an economic metal recovery. On the other hand, increasing environmental consciousness as well as limitations of classical methods require innovative recycling methodologies in order to enable a circular economy. Modern biotechnologies can contribute to solve some of the problems related to metal recycling. These approaches use natural properties of organisms, bio-compounds, and biomolecules to interact with minerals, materials, metals, or metal ions such as surface attachment, mineral dissolution, transformation, and metal complexation. Further, modern genetic approaches, e.g. realized by synthetic biology, enable the smart design of new chemicals. The article presents some recent developments in the fields of bioleaching, biosorption, bioreduction, and bioflotation, and their use for metal recovery from different waste materials. Currently only few of these developments are commercialized. Major limitations are high costs in comparison to conventional methods and low element selectivity. The article discusses future trends to overcome these barriers. Especially interdisciplinary approaches, the combination of different technologies, the inclusion of modern genetic methods, as well as the consideration of existing, yet unexplored natural resources will push innovations in these fields.     

Metavinculin: New insights into functional properties of a muscle adhesion protein

Metavinculin is a muscle-specific splice variant of the ubiquitously expressed cytoskeletal adaptor protein vinculin. Both proteins are thought to be co-expressed in all muscle types where they co-localize to microfilament-associated adhesion sites. It has been shown that a metavinculin-specific insertion of 68 amino acids alters the biochemical properties of the five-helix bundle in the tail domain. Here, we demonstrate that the metavinculin-specific helix H1′ plays an important role for protein stability of the tail domain, since a point mutation in this helix, R975W, which is associated with the occurrence of dilated cardiomyopathy in man, further decreases thermal stability of the metavinculin tail domain. In striated muscle progenitor cells (myoblasts), both, metavinculin and the R975W mutant show significantly reduced, albeit distinctive residency and exchange rates in adhesion sites as compared to vinculin. In contrast to previous studies, we show that metavinculin is localized in a muscle fiber type-dependent fashion to the costameres of striated muscle, reflecting the individual metabolic and physiological status of a given muscle fiber. Metavinculin expression is highest in fast, glycolytic muscle fibers and virtually absent in M. diaphragmaticus, a skeletal muscle entirely lacking fast, glycolytic fibers. In summary, our data suggest that metavinculin enrichment in attachment sites of muscle cells leads to higher mechanical stability of adhesion complexes allowing for greater shear force resistance.     

Investigating the Effect of Familiarity on Kin Recognition of Three‐Spined Stickleback (Gasterosteus aculeatus)

The ability to discriminate between related and unrelated individuals has been demonstrated in many species. The mechanisms behind this ability might be manifold and depend on the ecological context in which the species lives. In brood‐caring species, both familiarity and phenotype matching are known to be used in kin recognition. However, results of studies disentangling these two phenomena have proved contradictory. We aimed to broaden our knowledge about the mechanisms of kin recognition using shoaling preferences of three‐spined stickleback (Gasterosteus aculeatus) as a model behavior. In our first experiment, focal fish had the choice to shoal either with kin or unfamiliar non‐kin. In half of the trials, kin groups were composed of familiar individuals, while they were unfamiliar in the other half. Focal fish significantly preferred kin as shoaling partner, a result which was not reinforced by familiarity. In our second experiment, focal fish were given the choice between a shoal of familiar kin and a shoal of unfamiliar kin. Here, focal fish did not show any significant preference. These results indicate that familiarity does not impact stickleback's ability to recognize kin. Furthermore, they show that familiarity does not overrule recognition based on phenotype matching or innate recognition, underlining the importance of these mechanisms. Finally, our results lead to the assumption that individual recognition might play a minor role also in non‐kin‐based preferences for familiars.     

In vitro reconstitution of an mRNA-transport complex reveals mechanisms of assembly and motor activation

The assembly and composition of ribonucleic acid (RNA)–transporting particles for asymmetric messenger RNA (mRNA) localization is not well understood. During mitosis of budding yeast, the Swi5p-dependent HO expression (SHE) complex transports a set of mRNAs into the daughter cell. We recombinantly reconstituted the core SHE complex and assessed its properties. The cytoplasmic precomplex contains only one motor and is unable to support continuous transport. However, a defined interaction with a second, RNA-bound precomplex after its nuclear export dimerizes the motor and activates processive RNA transport. The run length observed in vitro is compatible with long-distance transport in vivo. Surprisingly, SHE complexes that either contain or lack RNA cargo show similar motility properties, demonstrating that the RNA-binding protein and not its cargo activates motility. We further show that SHE complexes have a defined size but multimerize into variable particles upon binding of RNAs with multiple localization elements. Based on these findings, we provide an estimate of number, size, and composition of such multimeric SHE particles in the cell.     

Reduced Immunosuppressive Properties of Axitinib in Comparison with Other Tyrosine Kinase Inhibitors

The multikinase inhibitors sunitinib, sorafenib, and axitinib have an impact not only on tumor growth and angiogenesis, but also on the activity and function of immune effector cells. In this study, a comparative analysis of the growth inhibitory properties and apoptosis induction potentials of tyrosine kinase inhibitors on T cells was performed. Tyrosine kinase inhibitor treatment resulted in a dramatic decrease in T cell proliferation along with distinct impacts on the cell cycle progression. This was at least partially associated with an enhanced induction of apoptosis although triggered by distinct apoptotic mechanisms. In contrast to sunitinib and sorafenib, axitinib did not affect the mitochondrial membrane potential (Δψ_m) but resulted in an induction or stabilization of the induced myeloid leukemia cell differentiation protein (Mcl-1), leading to an irreversible arrest in the G₂/M cell cycle phase and delayed apoptosis. Furthermore, the sorafenib-mediated suppression of immune effector cells, in particular the reduction of the CD8⁺ T cell subset along with the down-regulation of key immune cell markers such as chemokine CC motif receptor 7 (CCR7), CD26, CD69, CD25, and CXCR3, was not observed in axitinib-treated immune effector cells. Therefore, axitinib rather than sorafenib seems to be suitable for implementation in complex treatment regimens of cancer patients including immunotherapy.     

Identification of Amino Acids Conferring Chain Length Substrate Specificities on Fatty Alcohol-forming Reductases FAR5 and FAR8 from Arabidopsis thaliana

Fatty alcohols play a variety of biological roles in all kingdoms of life. Fatty acyl reductase (FAR) enzymes catalyze the reduction of fatty acyl-coenzyme A (CoA) or fatty acyl-acyl carrier protein substrates to primary fatty alcohols. FAR enzymes have distinct substrate specificities with regard to chain length and degree of saturation. FAR5 (At3g44550) and FAR8 (At3g44560) from Arabidopsis thaliana are 85% identical at the amino acid level and are of equal length, but they possess distinct specificities for 18:0 or 16:0 acyl chain length, respectively. We used Saccharomyces cerevisiae as a heterologous expression system to assess FAR substrate specificity determinants. We identified individual amino acids that affect protein levels or 16:0-CoA versus 18:0-CoA specificity by expressing in yeast FAR5 and FAR8 domain-swap chimeras and site-specific mutants. We found that a threonine at position 347 and a serine at position 363 were important for high FAR5 and FAR8 protein accumulation in yeast and thus are likely important for protein folding and stability. Amino acids at positions 355 and 377 were important for dictating 16:0-CoA versus 18:0-CoA chain length specificity. Simultaneously converting alanine 355 and valine 377 of FAR5 to the corresponding FAR8 residues, leucine and methionine, respectively, almost fully converted FAR5 specificity from 18:0-CoA to 16:0-CoA. The reciprocal amino acid conversions, L355A and M377V, made in the active FAR8-S363P mutant background converted its specificity from 16:0-CoA to 18:0-CoA. This study is an important advancement in the engineering of highly active FAR proteins with desired specificities for the production of fatty alcohols with industrial value.     

Seeded strain‐like transmission of β‐amyloid morphotypes in APP transgenic mice

The polymorphic β‐amyloid lesions present in individuals with Alzheimer's disease are collectively known as cerebral β‐amyloidosis. Amyloid precursor protein (APP) transgenic mouse models similarly develop β‐amyloid depositions that differ in morphology, binding of amyloid conformation‐sensitive dyes, and Aβ40/Aβ42 peptide ratio. To determine the nature of such β‐amyloid morphotypes, β‐amyloid‐containing brain extracts from either aged APP23 brains or aged APPPS1 brains were intracerebrally injected into the hippocampus of young APP23 or APPPS1 transgenic mice. APPPS1 brain extract injected into young APP23 mice induced β‐amyloid deposition with the morphological, conformational, and Aβ40/Aβ42 ratio characteristics of β‐amyloid deposits in aged APPPS1 mice, whereas APP23 brain extract injected into young APP23 mice induced β‐amyloid deposits with the characteristics of β‐amyloid deposits in aged APP23 mice. Injecting the two extracts into the APPPS1 host revealed a similar difference between the induced β‐amyloid deposits, although less prominent, and the induced deposits were similar to the β‐amyloid deposits found in aged APPPS1 hosts. These results indicate that the molecular composition and conformation of aggregated Aβ in APP transgenic mice can be maintained by seeded conversion.     

Vortex Formation with a Snapping Shrimp Claw

Snapping shrimp use one oversized claw to generate a cavitating high speed water jet for hunting, defence and communication. This work is an experimental investigation about the jet generation. Snapping shrimp (Alpheus-bellulus) were investigated by using an enlarged transparent model reproducing the closure of the snapper claw. Flow inside the model was studied using both High-Speed Particle Image Velocimetry (HS-PIV) and flow visualization. During claw closure a channel-like cavity was formed between the plunger and the socket featuring a nozzle-type contour at the orifice. Closing the mechanism led to the formation of a leading vortex ring with a dimensionless formation number of approximate ΔT*≈4. This indicates that the claw might work at maximum efficiency, i.e. maximum vortex strength was achieved by a minimum of fluid volume ejected. The subsequent vortex cavitation with the formation of an axial reentrant jet is a reasonable explanation for the large penetration depth of the water jet. That snapping shrimp can reach with their claw-induced flow. Within such a cavitation process, an axial reentrant jet is generated in the hollow cylindrical core of the cavitated vortex that pushes the front further downstream and whose length can exceed the initial jet penetration depth by several times.     

Metal Ion Concentrations in Body Fluids after Implantation of Hip Replacements with Metal-on-Metal Bearing – Systematic Review of Clinical and Epidemiological Studies

Introduction

The use of metal-on-metal (MoM) total hip arthroplasty (THA) increased in the last decades. A release of metal products (i.e. particles, ions, metallo-organic compounds) in these implants may cause local and/or systemic adverse reactions. Metal ion concentrations in body fluids are surrogate measures of metal exposure.

Objective

To systematically summarize and critically appraise published studies concerning metal ion concentrations after MoM THA.

Methods

Systematic review of clinical trials (RCTs) and epidemiological studies with assessment of metal ion levels (cobalt, chromium, titanium, nickel, molybdenum) in body fluids after implantation of metalliferous hip replacements. Systematic search in PubMed and Embase in January 2012 supplemented by hand search. Standardized abstraction of pre- and postoperative metal ion concentrations stratified by type of bearing (primary explanatory factor), patient characteristics as well as study quality characteristics (secondary explanatory factors).

Results

Overall, 104 studies (11 RCTs, 93 epidemiological studies) totaling 9.957 patients with measurement of metal ions in body fluids were identified and analyzed. Consistently, median metal ion concentrations were persistently elevated after implantation of MoM-bearings in all investigated mediums (whole blood, serum, plasma, erythrocytes, urine) irrespective of patient characteristics and study characteristics. In several studies very high serum cobalt concentrations above 50 µg/L were measured (detection limit typically 0.3 µg/L). Highest metal ion concentrations were observed after treatment with stemmed large-head MoM-implants and hip resurfacing arthroplasty.

Discussion

Due to the risk of local and systemic accumulation of metallic products after treatment with MoM-bearing, risk and benefits should be carefully balanced preoperatively. The authors support a proposed „time out“ for stemmed large-head MoM-THA and recommend a restricted indication for hip resurfacing arthroplasty. Patients with implanted MoM-bearing should receive regular and standardized monitoring of metal ion concentrations. Further research is indicated especially with regard to potential systemic reactions due to accumulation of metal products.     

On the Challenge of Fitting Tree Size Distributions in Ecology

Patterns that resemble strongly skewed size distributions are frequently observed in ecology. A typical example represents tree size distributions of stem diameters. Empirical tests of ecological theories predicting their parameters have been conducted, but the results are difficult to interpret because the statistical methods that are applied to fit such decaying size distributions vary. In addition, binning of field data as well as measurement errors might potentially bias parameter estimates. Here, we compare three different methods for parameter estimation – the common maximum likelihood estimation (MLE) and two modified types of MLE correcting for binning of observations or random measurement errors. We test whether three typical frequency distributions, namely the power-law, negative exponential and Weibull distribution can be precisely identified, and how parameter estimates are biased when observations are additionally either binned or contain measurement error. We show that uncorrected MLE already loses the ability to discern functional form and parameters at relatively small levels of uncertainties. The modified MLE methods that consider such uncertainties (either binning or measurement error) are comparatively much more robust. We conclude that it is important to reduce binning of observations, if possible, and to quantify observation accuracy in empirical studies for fitting strongly skewed size distributions. In general, modified MLE methods that correct binning or measurement errors can be applied to ensure reliable results.